Method and apparatus for producing two-piece can bodies from a laminated metal sheet and a two-piece can body produced thereby

ABSTRACT

A method and apparatus for producing two-piece can bodies by drawing and ironing a laminated metal sheet, and more particularly to a processing method which prevents abrasion damage or scuffing of the laminate layer on the can body during its ironing, and a drawn and ironed two-piece can body produced thereby.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for producing two-piececan bodies by drawing and ironing a laminated metal sheet, and moreparticularly to a processing method which prevents abrasion damage orscuffing of the laminate layer on the can body during its ironing, and adrawn and ironed two-piece can body produced thereby.

BACKGROUND OF THE INVENTION

Laminated metal sheet for packaging comprises a metal sheet and alaminate layer that covers one or both sides of the metal sheet wherethe laminate layer is produced by laminating the laminate layer onto themetal sheet by heat bonding or by direct extrusion onto the metal sheet.The laminate layer comprises one or more thermoplastic polymer layers.

Laminated metal sheet is used in the production of two-piece cans. Sucha can consists of a can body comprising a base and a tubular body fromsheet metal which is coated on at least one side with a laminate layerand a lid which is joined to the can body.

For the production of the can body a disc (usually circular) is producedfrom the laminated metal sheet, which disc is then deep-drawn into a cupwhich has a laminate layer at least on the outside, after which this cupis formed into a can body by wall ironing, the wall ironing taking placein a single stroke by punching the cup successively through a redrawring and one or more wall-ironing rings (see FIG. 1 ) using a punch in adrawing and ironing machine. The external shape of a punch is typicallycylindrical, and thus rotation-symmetric, and may have the same diameterover the operative part, or the punch may have different diameters overthe operative part, such as in JP2000042644, EP0402006, WO2019154743,GB2547016.

A separate punch typically is removably secured on the leading end of areciprocating ram in a drawing and ironing machine. The punch providesan inner mandrel on which the can is shaped, drawn, and ironed as itpasses through the one or more wall-ironing rings. The temperature ofthe punch increases due to the heat generated by the repeated frictionalcontact between the punch, the inside of the can body, and the one ormore wall-ironing rings past which the punch moves. During wall ironingthe shear forces can become excessively high in the laminate layeritself. This excessive shear results in an increased risk of damagingthe laminate layer. One type of damage is so-called scuffing orabrasion, which damages the laminate layer and may result in directcontact between the metal substrate and the wall ironing tooling and/ora visually unacceptable laminate layer finish or, in very severe cases,rupture of the can body wall. Adequate lubrication between the wallironing tooling and the laminate layer is important to prevent scuffingor abrasion damage, and this lubrication can be provided by the polymerlayer itself (dry process). However, because of the deformation processthe temperature of the metal sheet, the laminate layer, the redraw- andironing rings and the punch rises. The risk of damaging the laminatelayer increases if the temperature of the laminate layer increases.Consequently the temperature of the wall-ironing tooling must be keptbelow a critical value where the risk of damaging the laminate layerstarts to occur, and this means that the production rate of the draw-and wall-ironing is limited thereby. This critical value is dependent onthe composition of the laminate layer. In conventional can formation,externally applied cooling fluids maintain operational temperatureconditions. However, in the dry DWI process no externally appliedcooling fluids are used because the externally applied cooling fluidsmay contaminate the container surfaces which would then requirepost-forming cleaning processes that are costly and may beenvironmentally undesirable.

US2030084699 discloses a punch assembly comprising means to providecoolant to a circumferential channel that enables cooling the interiorsurface of the punch that is disposed at the end of a reciprocating ramin a drawing and ironing machine. However, application of this punchassembly is still found to cause abrasion damage and scuffing of the canbodies, especially at high reduction and high-speed production of canbodies.

OBJECTIVES OF THE INVENTION

It is an object of the invention to provide a method for producing canbodies for two-piece cans produced from laminated metal sheet withoutabrasion damage or scuffing of the laminate layer.

It is an also an object of the invention to provide a method forproducing can bodies for two-piece cans produced from laminated metalsheet at higher speeds/reductions without abrasion damage or scuffing ofthe laminate layer.

It is also an object of the invention to provide a method for producingcan bodies for two-piece cans without scuffing of the laminate layer atincreased production speed.

It is also an object of the invention to provide an apparatus forproducing can bodies according to the invention.

DESCRIPTION OF THE INVENTION

One or more of the objects is reached with a method according to claim1: A method for producing can bodies comprising a base and a tubularbody for two-piece cans, from a laminated metal sheet by deep drawingand wall-ironing, wherein a disc is produced from the laminated metalsheet, which is deep-drawn into a cup, followed by redrawing the cup andsubsequently forming the redrawn cup into a can body by wall ironing,wherein the wall ironing taking place in a single stroke by punching theredrawn cup through one or more wall-ironing rings by means of aninternally cooled punch assembly, wherein the punch assembly comprises

-   -   a ram (14),    -   a punch (1) which is, preferably removably, attached to the ram,        the punch assembly comprising an internal annular cavity (15)        below the surface of the punch between a position near the        distal end of the punch (15 a) and a position near the proximal        end of the punch (15 b),    -   a plurality of cooling fluid inlets (16) for supplying a cooling        fluid into the internal annular cavity and a plurality of        cooling fluid outlets (17) for removing the cooling fluid from        the internal annular cavity, wherein the internal annular cavity        is provided with means for improving the efficiency of the        internal cooling of the punch,    -   wherein the means for improving the efficiency of the internal        cooling of the punch consist of obstacles (18) in the internal        annular cavity to increase the turbulence in the cooling fluid        during its travel from the cooling fluid inlets to the cooling        fluid outlets and to provide a larger cooling surface for        extracting heat from the punch, wherein the obstacles consist of        -   discontinuous obstacles (18) such as chevrons, cylinders,            discontinuous walls or discontinuous zigzag walls, or of        -   continuous obstacles (18) in the form of a plurality of            adjacent helical walls delimiting a plurality of helical            cooling channels in the internal annular cavity to conduct            the cooling fluid from the cooling fluid inlets to the            cooling fluid outlets,    -   the ram comprising means for supplying cooling fluid to the        cooling fluid inlets and removing cooling fluid from the cooling        fluid outlets,        to efficiently internally cool the punch during the production        of the can bodies to prevent abrasion damage or scuffing of the        laminate layer on the tubular body of the can body, wherein    -   a. the cooling fluid inlets are arranged nearer the distal end        of the punch and wherein the cooling fluid outlets are arranged        nearer the proximal end of the punch, preferably wherein the        inlets and outlets are arranged in a regular pattern around the        circumference of the punch, or wherein    -   b. the cooling fluid inlets are arranged nearer the proximal end        of the punch and wherein the cooling fluid outlets are arranged        nearer the distal end of the punch, preferably wherein the        inlets and outlets are arranged in a regular pattern around the        circumference of the punch, or wherein    -   c. the cooling fluid inlets of part of the helical cooling        channels are arranged nearer the distal end of the punch and        wherein the corresponding cooling fluid outlets are arranged        nearer the proximal end of the punch, and wherein the cooling        fluid inlets of the other helical cooling channels are arranged        nearer the proximal end of the punch and wherein the        corresponding cooling fluid outlets are arranged nearer the        distal end of the punch, so that some of the helical cooling        channels conduct cooling fluid from the distal end to the        proximal end of the punch and the other cooling channels conduct        cooling fluid from the proximal end to the distal end of the        punch, preferably wherein the direction of the cooling fluid        alternates from one helical cooling channel to its adjacent        helical cooling channel, preferably wherein the inlets and        outlets are arranged in a regular pattern around the        circumference of the punch.

The invention therefore embodies three different variants: a, b and c.Variant a and b are different in their location of the inlets andoutlets for the cooling liquid in the internal annular cavity with thediscontinuous obstacles or the continuous obstacles (helical coolingchannels).

Variant c relates only to the embodiment wherein the internal annularcavity is provided with continuous obstacles in the form of helicalcooling channels.

Preferable embodiments are provided in the dependent claims.

The punch is attached to the end of the ram. Preferably the punch isremovably attached to the ram. This means that the punch, which outsidesurface contacts the can body directly, can be replaced without the needto replace the ram, e.g. if the punch is worn or damaged. However, theinvention is also embodied by the ram and the punch forming one integralpart, i.e. wherein the punch is not removably attached to the ram, andwherein the internal annular cavity forms a cavity in the integralram&punch combination. If the punch portion is welded to the ram, thenthe punch is considered to form an integral part of the ram&punchcombination, because the punch cannot be easily removed from the ram anylonger. In such a construction the ram&punch combination must bereplaced if the punch portion is worn or damaged.

In case the punch is removably attached then obstacles in the internalannular cavity preferably are part of the punch, and thus the obstaclesare removed with the punch when the punch is removed. Less preferablythe obstacles are formed directly on the ram, and thus the obstaclesstay behind on the ram if the punch is removed from the ram. These twoembodiments are morphologically identical when the punch is mounted onthe ram.

The method according to the invention is based on the improvement of theinternal cooling of the punch assembly by increasing the coolingefficiency. This is achieved by increasing the degree of turbulence inthe cooling fluid being passed through the punch and by increasing thecontact surface between the cooling fluid and the punch. The way theinvention achieves the increase in turbulence in the cooling fluid andincreasing the contact surface between the cooling fluid and the punchis by placing discrete or continuous obstacles in the internal annularcavity. The punch comprises an internal annular cavity that extends overa length of the punch just below the surface of the punch that comesinto contact with the side walls of the can bodies during the wallironing step. The distance between the surface of the punch and theinternal annular cavity, i.e. the wall thickness, has to be thick enoughto withstand the mechanical stresses of the deep drawing andwall-ironing process and maintain its dimensions, but also thin enoughto maximise the heat transfer from the surface of the internal annularto the cooling fluid running through the cavity. Through this internalannular cavity the cooling fluid can be led from cooling fluid inlets atone end of the internal annular cavity to the cooling fluid outlets atthe other end of the internal annular cavity. This way heat can be ledaway from the punch by the cooling fluid, and the surface temperature ofthe punch can be kept below the critical value to prevent scuffing orabrasion damage. In the absence of any obstacles in the internal annularcavity, which is the prior art situation, the cooling fluid flowsbetween the cooling fluid inlets and outlets directly and laminarly.This means that the cooling fluid has little time to absorb heat, andalso as a result of the laminar flow, the cooling capacity of thecooling fluid is not efficiently used. It is noted that usually theredraw ring and ironing rings also have internal cooling channels, whichcool the outside laminate layer of the can body. However, the majorityof the heat will be dissipated by the cooled punch, because this has amuch longer time of contact and a much larger area of contact with thelaminate layer.

The cooling fluid is not particularly limiting. Water, preferablydemineralised water, has proven to be very suitable. Anti-corrosionagents may be added to the cooling fluid.

The obstacles break-up the flow of the cooling fluid and also increasethe cooling surface of the punch, so the ability to pass on the heatfrom the punch into the cooling fluid increases both as a result of theincrease in cooling surface and the increase in turbulence, because aturbulent flow is able to absorb more heat than a laminar flow can.

In an embodiment of the invention the discontinuous obstacles in theinternal annular cavity may for instance comprise of pillars(cylindrical or otherwise), chevrons, discontinuous short walls whichare perpendicular or angled to the flow of the cooling fluid through thecavity, or discontinuous zig zag walls. The external shape of the punchis preferably rotation-symmetrical with respect to the centreline of theram.

The continuous obstacles prolong the contact time between the coolingfluid and the punch because the obstacles force the cooling fluid totake a longer path between the cooling fluid inlets and the coolingfluid outlets, and the contact surface of the internal annular cavitybecomes larger as a result of the presence of the discontinuousobstacles in the internal annular cavity. Also, as a consequence of thepath being longer due to the presence of the continuous obstacles, thearea through which the cooling fluid has to flow becomes smaller, andthis in turn increases the turbulence in the fluid.

The method according to the invention therefore results in a moreefficient cooling of the punch and therefore of a lower surfacetemperature of the punch in comparison to the prior art punches. Thecooler punch temperature results in lower laminate layer temperaturesduring the wall-ironing process, and thus prevents scuffing or abrasiondamage in laminate layers prone to such damage, and enables increasingthe production speed of the can bodies because the punch temperature atwhich the risk for scuffing or abrasion damage in laminate layersbecomes prominent is reached at higher production speeds compared to theprior art situation.

In one embodiment of the invention (variant a) the cooling fluid inletsare arranged nearer the distal end of the punch and the cooling fluidoutlets are arranged nearer the proximal end of the punch. Preferablythe inlets and outlets are arranged in a regular pattern around thecircumference of the punch. In another embodiment of the invention(variant b) the cooling fluid inlets are arranged nearer the proximalend of the punch and wherein the cooling fluid outlets are arrangednearer the distal end of the punch, preferably wherein the inlets andoutlets are arranged in a regular pattern around the circumference ofthe punch. In variant a and b the means for improving the efficiency ofthe internal cooling of the punch consist of discontinuous obstacles orconsist of continuous obstacles in the form of a plurality of adjacenthelical walls delimiting a plurality of helical cooling channels in theinternal annular cavity.

In another embodiment of the invention (variant c) the continuousobstacles are helical walls in the internal annular cavity thus forminghelical cooling channels in the internal annular cavity. In thisembodiment part of the cooling fluid inlets are arranged nearer thedistal end of the punch and wherein the other cooling fluid inlets arearranged nearer the proximal end of the punch, so that some of thehelical cooling channels conduct cooling fluid from the distal end tothe proximal end of the punch and the other cooling channels conductcooling fluid from the proximal end to the distal end of the punch,preferably wherein the direction of the cooling fluid alternates fromone helical cooling channel to its adjacent helical cooling channel.

It is noted that helix is a shape like a spiral staircase. It is a typeof smooth space curve with tangent lines at a constant angle to a fixedaxis. A circular helix of radius a and slope b/a (or pitch 2 nb) isdescribed by the following parametrisation:

x(t) = a · cos(t) y(t) = a · sin(t) z(t) = b · t

According to the invention the number of helical continuous obstaclesmust be such that a plurality, and preferably at least three helicalcooling channels are formed. It is preferable that each helical coolingchannel is provided with its own cooling fluid inlet and its own coolingfluid outlet. The inventors found that three or more helical coolingchannels leads to a very efficient cooling because the length of thechannels is such that the cooling fluid is able to effectively andefficiently cool the work surface of the punch. With one or two coolingchannels the efficiency of the cooling is significantly reduced and thedanger of scuffing or abrasion damage of the laminate layers increases.Preferably the punch comprises at least four adjacent helical coolingchannel, more preferably at least five adjacent helical cooling channeland even more preferably at least six adjacent helical cooling channels.The inventors found that six channels resulted in an optimal combinationof cooling capacity without excessively complicating the design of thepunch. Preferably the inlets and outlets for the cooling fluid arearranged in a regular pattern around the circumference of the punch,i.e. 60° between each inlet or outlet around the circumference for thesix-channel embodiment, or 72° for a five-channel embodiment. Althoughit is possible to feed more than one helical channel with one inlet orbleed more than one helical channel with one outlet, it is preferablethat each channel is fed with its own cooling fluid inlet and bled withits own cooling fluid outlet. Individual inlets and outlets for coolingfluid also allows to alternate the flow direction between adjacenthelical cooling channels, thereby potentially achieving an even morehomogeneous cooling of the punch.

The advantage of inlets being arranged at the distal end or the proximalend of the punch, and the corresponding outlets being arranged at theproximal end or the distal end of the punch means that the coolingliquid only travels directly from the inlet at one end of the punch tothe other end so that the maximum cooling effect can be achieved. Inprior art such as JP2006055860, JP2006-055860 and JP2005-288483 thecooling liquid has to travel up and down the punch because the inletsand outlets for the cooling liquid are all located at the proximal endof the punch. JP2006055860 discloses a punch with continuous zig-zagchannels, whereas 3P2006-055860 and 3P2005-288483 show an embodimentwith a single helical channel and embodiments with or continuous zig-zagchannels through which the cooling liquid is led.

In prior art such as JP2006055860, JP2006-055860 and JP2005-288483 thereturning warmed-up cooling liquid meets cooler cooling liquid therebyheating the incoming cooling liquid. This diminishes the coolingcapacity of the incoming cooling liquid and thereby reduces the coolingefficiency of the cooled punch as a whole. So these prior artconfigurations have a very considerably reduced cooling capacitycompared to the configurations according to the invention.

The external temperature of the punch can be monitored continuously,e.g. by direct contact or contactless measurement of the punchtemperature or by monitoring the temperature of the cooling fluidentering and leaving the punch. In an embodiment of the invention thetemperature of the punch assembly is controlled by means of atemperature control unit wherein the temperature control unit is able tocontrol the temperature of the punch by adapting the speed of productionof can bodies and/or by adapting the flow rate of the cooling fluidentering the internal annular cavity and/or by adapting the temperatureof the cooling fluid entering the internal annular cavity.

In an embodiment the redraw ring and the one or more ironing rings alsohave internal cooling channels, which enable cooling the outsidelaminate layer of the can body during the deep drawing and wall-ironing.

The invention is also embodied in the punch assembly according to claim6. Preferable embodiments are provided in the dependent claims.

The punch according to the invention may be provided with the obstaclesin two ways. Since the internal annular cavity provided with thediscontinuous or continuous obstacles is quite complicated structurally,it is preferable to produce the punch by means of additivemanufacturing, such as 3D-printing. By means of additive manufacturingthe punch with the external surface contacting (in use) the laminatelayer of the can bodies, including the complicated internal structure inthe internal annular cavity can be produced as one integral part, in oneproduction step. For instance, the punch as depicted in FIG. 4 may beproduced in one production step by additive manufacturing so that thepunch sleeve 19 and the insert 20 can be made as one part where thesleeve and insert are combined, and therefore inseparable, in one part,i.e. one integral part. The channels or obstacles in the internalannular cavity are produced simultaneously with the rest of the punch asthe punch is being produced by additive manufacturing. The production ofsuch a punch with the intricate shapes of the discontinuous obstacles inthe internal annular cavity cannot be produced by classical machining inone part, i.e. one integral part.

As an alternative the punch can be produced from at least two parts: apunch sleeve and an insert which, when joined together form the internalannular cavity with the discrete or continuous obstacles, e.g. theadjacent helical channels. The insert with the obstacles can be producedby additive manufacturing (AM) wherein the insert also may comprise thecooling fluid inlets and the cooling fluid outlets from a materialsuitable for AM such as a tool steel, a cemented carbide, such as WC, orcopper or a copper alloy. Alternatively the insert may be produced bymachining the insert, for instance from a tool steel or another suitablematerial such as stainless steel, copper or a copper alloy.

The material of the punch with the integral internal structure in theinternal annular cavity or the insert with the discrete or continuousobstacles in the internal annular cavity (after assembly with the punchsleeve) preferably is a material suitable for AM such as a cementedcarbide, such as WC, or copper or a copper alloy.

The invention is also embodied in a can body produced in accordance withthe method or apparatus according to the invention.

Laminated metal sheet for packaging comprises a metal sheet and alaminate layer that covers at least one side of the metal sheet. Such alaminated metal sheet is produced by laminating the laminate layer ontothe metal sheet. The laminate layer may be applied to the metal sheet byheat bonding the laminate layer to the metal sheet or by using anadhesion promoter between the laminate layer and the metal sheet or byusing a laminate layer comprising an adhesion layer. The laminate layermay be produced in-line and laminated onto the metal sheet in anintegrated lamination step, or a pre-produced laminate layer may belaminated onto the metal sheet in a separate lamination process step. Analternative lamination method is to extrude a laminate layer by means ofa flat die and laminate the laminate layer directly onto the metalsheet.

The ironing method of the present invention is particularly effectivefor ironing a metal sheet, selected from the group of metal sheets suchas cold rolled steel, blackplate, tinplate, ECCS, TCCT®, galvanisedsteel or aluminium or aluminium alloy. The metal sheet is preferablysupplied in coiled form.

The metal sheet is preferably coated on one or both sides with anorganic resin selected from polyester, polyolefin, polyamide and otherthermoplastic resins. The resin film to which the present invention isapplicable may be a film formed by a single layer, or two or morelayers, and is preferably a film of a thermoplastic resin, especially apolyester resin.

The polyester resin preferably has an ester unit such as ethyleneterephthalate, ethylene isophthalate, butylene terephthalate or butyleneisophthalate, and is preferably a polyester consisting mainly of atleast one kind of ester unit selected therefrom. Each ester unit may bea copolymer, or the polyester may be a blend of homopolymers orcopolymers of two or more kinds of ester units. It is also possible touse other ester units containing e.g. naphthalenedicarboxylic acid,adipic acid, sebacic acid or trimellitic acid as their acid component,or e.g. propylene glycol, diethylene glycol, neopentyl glycol,cyclohexanedimethanol or pentaerythritol as their alcohol component.

The polyester may be a laminate of two or more polyester layers composedof homopolyesters or copolyesters, or a blend of two or more thereof.For example, the polyester film may have a copolymerized polyester layerof high thermal adhesion as a lower layer, and a polyester or modifiedpolyester layer of high strength, heat resistance and barrier propertyagainst corrosive substances as an upper layer.

The resin film preferably has a thickness of 5 to 100 μm and morepreferably 10 to 40 μm when it is a single-layer film. Any film having athickness below 5 μm is very difficult to laminate on a surface-treatedsteel sheet, is likely to give a defective resin layer upon drawing, ordrawing and ironing and is unsatisfactory in impermeability to corrosivesubstances when a can is formed and filled with its contents. Anincrease in thickness gives satisfactory impermeability, but anythickness over 100 μm is economically a disadvantage. The proportions inthickness of the layers of a multi-layer film depend on formability,impermeability, etc., and the thicknesses of the layers are socontrolled as to give a total thickness of 5 to 60 μm.

The resin film may be formed from a resin to which a colouring pigment,a stabilizer, an oxidation inhibitor, a lubricant, etc. have been addedto the extent not impairing the necessary properties thereof. It ispossible to use a metal sheet having a pigment-free polyester resin filmlaminated on its side supposed to define the inner surface of a can,while a polyester resin film containing a pigment, such as titaniumoxide, is laminated on its side supposed to define the outer surface ofthe can.

DRAWINGS AND FIGURES

The invention is further described by means of the following,non-limiting drawings and figures.

FIG. 1 illustrates how a preformed deep-drawn cup 3 is formed into afinished wall-ironed can body 9. The cup 3 is placed between a redrawsleeve 2 and a redraw die 4. When punch 1 moves to the right, the cup 3is brought to an internal diameter of the final finished can 9 by theredrawing step. Then, the punch 1 successively forces the productthrough (in this example) two wall-ironing rings 6 and 7. Ring 8 is anoptional stripper ring. Wall ironing provides the can body 9 to beformed with its ultimate wall thickness and wall length. Finally, thebase of can body 9 is formed by moving punch 1 towards an optional basetool 10. Retracting punch 1 allows to detach can 9 from the punch 1 sothat it can be discharged in the transverse direction. The optionalstripper ring may assist in this. The can 9 is then subsequentlytrimmed, optionally necked, flanged and provided with a lid afterfilling.

FIG. 2 provides a detailed illustration of the passage of a part of thecan wall to be formed through, for example, wall-ironing ring 6. Punch 1is indicated diagrammatically. The entry plane for wall-ironing ring 6runs at an entry angle α to the direction of the axis of thewall-ironing ring. The thickness of the material of the wall to beformed is reduced between punch 1 and wall-ironing ring 6. This materialcomprises the actual metal can body wall 11 with laminate layers 12 and13 on either side. The laminate layer 12 becomes the outside of the canbody, and the laminate layer 13 becomes the inside of the can body,eventually coming into contact with the contents of the can. The figureillustrates how the thickness of all three layers 11, 12 and 13 isreduced.

FIG. 3 shows the punch 1 which typically is removably secured on theleading end of a reciprocating ram 14 in a drawing and ironing machine.FIG. 3 shows the punch on top of the ram in one of the embodiments ofthe invention in detail. The internal annular cavity runs between 15 aand 15 b and is more prominently outlined in FIG. 4 with the dashedboxes in the cross section of the punch.

FIG. 4 shows a cross-section of the punch with the continuous obstaclesforming the adjacent helical cooling channels. In this figure the punchconsists of a punch sleeve 19 and an insert 20. The internal annularcavity formed by the joined punch sleeve and insert is filled with thecontinuous obstacles.

FIG. 5 a shows the outside surface of the insert 20 with the helicalcontinuous obstacles 18. It shows six adjacent helical cooling channels(channel a-f), each with their own individual inlet and outlet forcooling fluid. FIG. 5 b shows a cross section of the same insert as usedin FIG. 4 .

FIG. 6 shows six different examples of the internal annular cavity:without obstacles (A: prior art); with discontinuous obstacles (B: shortwalls perpendicular to the flow of the cooling fluid; C: circularpillars; D: chevrons; E: zig zag channels); and with continuousobstacles (F: six adjacent helical cooling channels formed by thecontinuous obstacles forming the walls of the channels). The distancebetween the cooling fluid and the work surface of the punch is the samefor all embodiments.

FIG. 7 shows the surface temperature of the various examples. It isclear that all the examples according to the invention provide a veryhomogeneous temperature profile along the length of the punch (runningfrom about 40 to about 110 mm). The prior art shows a significantlyhigher surface temperature of the punch, showing the improvement thatthe invention is able to provide with regard to the surface temperatureof the punch. The lowest surface temperature is achieved with thecontinuous obstacles forming the helical channels, irrespective of theflow direction of the cooling fluid in the channels (distal to proximal,proximal to distal or mixed). All embodiments of the invention show asignificant improvement over the prior art.

FIG. 8 shows the effect of this lower surface temperature. The closedcircles show the temperature during the production of can bodies at 165cans/minute using the prior art annular internal cavity withoutobstacles. The triangles show the punch temperature at the sameproduction rate and identical boundary conditions for the embodimentwith the six adjacent helical cooling channels, and a steady statetemperature of about 65° C. is reached compared to 95° C. for the priorart punch. This means that the production rate can be increased. In theexample the production rate is increased 70% to 280 cans/minute and thisleads to a maximum temperature of the punch of just below 90° C., whichstill is below the prior art situation at a much lower production rate.The cans made at an increased production rate according to the method ofthe invention were free of scuffing and no abrasion damage was observed.

The results of the discontinuous obstacles are only marginally lessfavourable compared to the continuous obstacles and also allow asignificant improvement in surface temperature control and associatedproduction rate improvement of about 60-65%.

1. A method for producing can bodies comprising a base and a tubularbody for two-piece cans, from a laminated metal sheet by deep drawingand wall-ironing, wherein a disc is produced from the laminated metalsheet, which is deep-drawn into a cup, followed by redrawing the cup andsubsequently forming the redrawn cup into a can body by wall ironing,wherein the wall ironing taking place in a single stroke by punching theredrawn cup through one or more wall-ironing rings by means of aninternally cooled punch assembly, wherein the punch assembly comprises:a ram, a punch which is attached to the ram, the punch assemblycomprising an internal annular cavity below the surface of the punchbetween a position near the distal end of the punch and a position nearthe proximal end of the punch, a plurality of cooling fluid inlets forsupplying a cooling fluid into the internal annular cavity and aplurality of cooling fluid outlets for removing the cooling fluid fromthe internal annular cavity, wherein the internal annular cavity isprovided with means for improving the efficiency of the internal coolingof the punch, wherein the means for improving the efficiency of theinternal cooling of the punch consist of obstacles in the internalannular cavity to increase the turbulence in the cooling fluid duringits travel from the cooling fluid inlets to the cooling fluid outletsand to provide a larger cooling surface for extracting heat from thepunch, wherein the obstacles consist of: discontinuous obstacles such aschevrons, cylinders, or of continuous obstacles in the form of aplurality of adjacent helical walls delimiting a plurality of helicalcooling channels in the internal annular cavity to conduct the coolingfluid from the cooling fluid inlets to the cooling fluid outlets, theram comprising means for supplying cooling fluid to the cooling fluidinlets and removing cooling fluid from the cooling fluid outlets, toefficiently internally cool the punch during the production of the canbodies to prevent abrasion damage or scuffing of the laminate layer onthe tubular body of the can body, wherein a. the cooling fluid inletsare arranged nearer the distal end of the punch and wherein the coolingfluid outlets are arranged nearer the proximal end of the punch, orwherein b. the cooling fluid inlets are arranged nearer the proximal endof the punch and wherein the cooling fluid outlets are arranged nearerthe distal end of the punch, or wherein c. the cooling fluid inlets ofpart of the helical cooling channels are arranged nearer the distal endof the punch and wherein the corresponding cooling fluid outlets arearranged nearer the proximal end of the punch, and wherein the coolingfluid inlets of the other helical cooling channels are arranged nearerthe proximal end of the punch and wherein the corresponding coolingfluid outlets are arranged nearer the distal end of the punch, so thatsome of the helical cooling channels conduct cooling fluid from thedistal end to the proximal end of the punch and the other coolingchannels conduct cooling fluid from the proximal end to the distal endof the punch.
 2. The method according to claim 1, wherein the punchcomprises at least three adjacent helical cooling channels.
 3. Themethod according to claim 1, wherein each helical cooling channel isprovided with its own cooling fluid inlet and its own cooling fluidoutlet.
 4. The method according to claim 1, wherein the redraw ring andthe one or more ironing rings also have internal cooling channels, whichcool the outside laminate layer of the can body during the deep drawingand wall-ironing.
 5. The method according to claim 1, wherein thetemperature of the punch assembly is controlled by means of atemperature control unit and wherein the temperature control unit isable to control the temperature of the punch by adapting the speed ofproduction of can bodies and/or by adapting the flow rate of the coolingfluid entering the internal annular cavity and/or by adapting thetemperature of the cooling fluid entering the internal annular cavity.6. An internally cooled punch assembly for use in the method accordingto claim 1, wherein the punch assembly comprises: a ram, a punchattached to the ram, the punch assembly comprising an internal annularcavity below the surface of the punch between a position near the distalend of the punch and a position near the proximal end of the punch, aplurality of cooling fluid inlets for supplying a cooling fluid into theinternal annular cavity and a plurality of cooling fluid outlets forremoving the cooling fluid from the internal annular cavity, wherein theinternal annular cavity is provided with means for improving theefficiency of the internal cooling of the punch, wherein the means forimproving the efficiency of the internal cooling of the punch consist ofobstacles in the internal annular cavity to increase the turbulence inthe cooling fluid during its travel from the cooling fluid inlets to thecooling fluid outlets and to provide a larger cooling surface forextracting heat from the punch wherein the obstacles consist of:discontinuous obstacles or of continuous obstacles in the form of aplurality of adjacent helical walls delimiting a plurality of helicalcooling channels in the internal annular cavity to conduct the coolingfluid from the cooling fluid inlets to the cooling fluid outlets, theram comprising means for supplying cooling fluid to the cooling fluidinlets and removing cooling fluid from the cooling fluid outlets, toefficiently internally cool the punch during the production of the canbodies to prevent abrasion damage or scuffing of the laminate layer onthe tubular body of the can body, wherein a. the cooling fluid inletsare arranged nearer the distal end of the punch and wherein the coolingfluid outlets are arranged nearer the proximal end of the punch, orwherein b. the cooling fluid inlets are arranged nearer the proximal endof the punch and wherein the cooling fluid outlets are arranged nearerthe distal end of the punch, or wherein c. the cooling fluid inlets ofpart of the helical cooling channels are arranged nearer the distal endof the punch and wherein the corresponding cooling fluid outlets arearranged nearer the proximal end of the punch, and wherein the coolingfluid inlets of the other helical cooling channels are arranged nearerthe proximal end of the punch and wherein the corresponding coolingfluid outlets are arranged nearer the distal end of the punch, so thatsome of the helical cooling channels conduct cooling fluid from thedistal end to the proximal end of the punch and the other coolingchannels conduct cooling fluid from the proximal end to the distal endof the punch.
 7. The punch assembly according to claim 6, wherein thepunch comprising the internal annular cavity with the obstacles or theplurality of adjacent helical cooling channels is a product of additivemanufacturing.
 8. The punch assembly according to claim 7, wherein thepunch comprises a punch sleeve and an insert which, when assembled, formthe punch with the internal annular cavity with the obstacles.
 9. Thepunch assembly according to claim 8, wherein the insert with theobstacles a product of additive manufacturing.
 10. The punch assemblyaccording to claim 9, wherein the material of the insert is a machinedtool steel, wherein the obstacles are machined in the insert.
 11. Thepunch assembly according to claim 6, wherein the plurality of continuousobstacles forming the helical cooling channels runs between a positionnear the distal end of the punch to a position near the proximal end ofpunch and wherein the helical cooling channels run below the surface ofthe punch, and wherein the punch comprises at least three adjacenthelical cooling channels.
 12. The punch assembly according to claim 6,wherein the plurality of continuous obstacles forming the helicalcooling channels runs between a position near the proximal end of thepunch to a position near the distal end of punch and wherein the helicalcooling channels run below the surface of the punch, and wherein thepunch comprises at least three adjacent helical cooling channels. 13.The punch assembly according to claim 6, wherein the temperature of thepunch assembly is controlled by means of a temperature control unitwhich is able to control the temperature of the punch by adapting thespeed of production of can bodies and/or by adapting the flow rate ofthe cooling fluid entering the internal annular cavity and/or byadapting the temperature of the cooling fluid entering the internalannular cavity.
 14. A can body produced by the method according toclaim
 1. 15. The method according to claim 1, wherein the punch isremovably, attached to the ram, wherein the discontinuous obstacles areselected from chevrons, cylinders, discontinuous walls or discontinuouszigzag walls, wherein the cooling fluid inlets arranged nearer thedistal end of the punch, and the cooling fluid outlets arranged nearerthe proximal end of the punch, are arranged in a regular pattern aroundthe circumference of the punch, or wherein the cooling fluid inletsarranged nearer the proximal end of the punch, and the cooling fluidoutlets arranged nearer the distal end of the punch, are arranged in aregular pattern around the circumference of the punch, or wherein thecooling fluid inlets of part of the helical cooling channels arrangednearer the distal end of the punch and the corresponding cooling fluidoutlets are arranged nearer the proximal end of the punch, and thecooling fluid inlets of the other helical cooling channels are arrangednearer the proximal end of the punch and the corresponding cooling fluidoutlets are arranged nearer the distal end of the punch, so that some ofthe helical cooling channels conduct cooling fluid from the distal endto the proximal end of the punch and the other cooling channels conductcooling fluid from the proximal end to the distal end of the punch,wherein the direction of the cooling fluid alternates from one helicalcooling channel to its adjacent helical cooling channel, wherein theinlets and outlets are arranged in a regular pattern around thecircumference of the punch.
 16. The method according to claim 2, whereinthe punch comprises at least six adjacent helical cooling channels. 17.The punch according to claim 6, wherein the punch is removably, attachedto the ram, wherein the discontinuous obstacles are selected fromchevrons, cylinders, discontinuous walls or discontinuous zigzag walls,wherein the cooling fluid inlets arranged nearer the distal end of thepunch, and the cooling fluid outlets arranged nearer the proximal end ofthe punch, are arranged in a regular pattern around the circumference ofthe punch, or wherein the cooling fluid inlets arranged nearer theproximal end of the punch, and the cooling fluid outlets arranged nearerthe distal end of the punch, are arranged in a regular pattern aroundthe circumference of the punch, or wherein the cooling fluid inlets ofpart of the helical cooling channels arranged nearer the distal end ofthe punch and the corresponding cooling fluid outlets are arrangednearer the proximal end of the punch, and the cooling fluid inlets ofthe other helical cooling channels are arranged nearer the proximal endof the punch and the corresponding cooling fluid outlets are arrangednearer the distal end of the punch, so that some of the helical coolingchannels conduct cooling fluid from the distal end to the proximal endof the punch and the other cooling channels conduct cooling fluid fromthe proximal end to the distal end of the punch, wherein the directionof the cooling fluid alternates from one helical cooling channel to itsadjacent helical cooling channel, wherein the inlets and outlets arearranged in a regular pattern around the circumference of the punch. 18.The punch assembly according to claim 8, wherein the insert with theobstacles is a product of additive manufacturing wherein the insert alsocomprises the cooling fluid inlets and the cooling fluid outlets. 19.The punch assembly according to claim 9, wherein the material of theinsert is a machined tool steel, wherein the obstacles are machined inthe insert, and wherein the insert also comprises the cooling fluidinlets and the cooling fluid outlets.
 20. The punch assembly accordingto claim 6, wherein the plurality of continuous obstacles forming thehelical cooling channels runs between a position near the distal end ofthe punch to a position near the proximal end of punch and wherein thehelical cooling channels run below the surface of the punch, whereineach helical cooling channel is provided with its own cooling fluidinlet and its own cooling fluid outlet and wherein the punch comprisesat least six adjacent helical cooling channels.
 21. The punch assemblyaccording to claim 6, wherein the plurality of continuous obstaclesforming the helical cooling channels runs between a position near theproximal end of the punch to a position near the distal end of punch andwherein the helical cooling channels run below the surface of the punch,wherein each helical cooling channel is provided with its own coolingfluid inlet and its own cooling fluid outlet and wherein the punchcomprises at least six adjacent helical cooling channels.